"Our finding, that personality traits are 'contagious' among children, flies in the face of common assumptions that personality is ingrained and can not be changed," said Jennifer Watling Neal from Michigan State University in the US.
"This is important because some personality traits can help children succeed in life, while others can hold them back," said Neal.
The researchers studied two preschool classes for an entire school year, analysing personality traits and social networks for one class of three-year-olds and one class of four-year-olds.
Children whose play partners were overanxious and easily frustrated, however, did not take on these particular traits.
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The study is the first to examine these personality traits in young children over time.
Emily Durbin, associate professor at Michigan State University said kids are having a bigger effect on each other than people may realise.
"Parents spend a lot of their time trying to teach their child to be patient, to be a good listener, not to be impulsive," said Durbin.
"However this was not their parents or their teachers affecting them - it was their friends. It turns out that three- and four-year-olds are being change agents," Durbin added.